DESCRIPTION: The purpose of this proposal is to isolate genes involved in autistic disorder (AD). The gene hunt will focus on chromosome 15q11-q13 because of recent evidence, some of it from the investigator's laboratory, that this region is linked to AD. The first set of aims is to develop markers from genomic contigs to genetically fine map the region in AD families in order to define regions of high recombination as closely as possible and determine the most likely location of the AD locus. The families will also be examined for methylation abnormalities and chromosomal duplications, insertion, deletions, or inversions. The second set of aims revolves around the isolation and analysis of AD candidate genes for direct identification of causative mutations.